Neuropathic pain

Neuromolecular and behavioral effects of cannabidiol on depressive-associated behaviors and neuropathic pain conditions in mice

BACKGROUND AND AIMS

Neuropathic pain (NP) has a high incidence in the general population, is closely related to anxiety disorders, and has a negative impact on the quality of life. Cannabidiol (CBD), as a natural product, has been extensively studied for its potential therapeutic effects on symptoms such as pain and depression (DP). However, the mechanism of CBD in improving NP with depression is not fully understood.

METHODS

First, we used bioinformatics tools to deeply mine the intersection genes associated with NP, DP, and CBD. Secondly, the core targets were screened by Protein-protein interaction network, Gene Ontology, Kyoto Encyclopedia of Genes and Genomes analysis, molecular docking and molecular dynamics simulation. Next, the effects of CBD intervention on pain and depressive behaviors in the spinal nerve ligation (SNL) mouse model were evaluated using behavioral tests, and dose-response curves were plotted. After the optimal intervention dose was determined, the core targets were verified by Western blot (WB) and Quantitative Polymerase Chain Reaction (qPCR). Finally, we investigated the potential mechanism of CBD by Nissl staining, Immunofluorescence (IF) and Transmission Electron Microscopy (TEM).

RESULTS

A total of five core genes of CBD most associated with NP and DP were screened by bioinformatics analysis, including PTGS2, GPR55, SOD1, CYP1A2 and NQO1. Behavioral test results showed that CBD by intraperitoneal administration 5 mg/kg can significantly improve the pain behavior and depressive state of SNL mice. WB, qPCR, IF, and TEM experiments further confirmed the regulatory effects of CBD on key molecules.

CONCLUSION

In this study, we found five targets of CBD in the treatment of NP with DP. These findings provide further theoretical and experimental basis for CBD as a potential therapeutic agent.

Advances in the use of local anesthetic extended-release systems in pain management

Pain management remains among the most common and largely unmet clinical problems today. Local anesthetics play an indispensable role in pain management. The main limitation of traditional local anesthetics is the limited duration of a single injection. To address this problem, catheters are often placed or combined with other drugs in clinical practice to increase the time that local anesthetics act. However, this method does not meet the needs of clinical analgesics. Therefore, many researchers have worked to develop local anesthetic extended-release types that can be administered in a single dose. In recent years, drug extended-release systems have emerged dramatically due to their long duration and efficacy, providing more possibilities for the application of local anesthetics. This paper summarizes the types of local anesthetic drug delivery systems and their clinical applications, discusses them in the context of relevant studies on local anesthetics, and provides a summary and outlook on the development of local anesthetic extended-release agents.

Negative allosteric modulator of Group Ⅰ mGluRs: Recent advances and therapeutic perspective for neuropathic pain

Neuropathic pain (NP) is a widespread public health problem that existing therapeutic treatments cannot manage adequately; therefore, novel treatment strategies are urgently required. G-protein-coupled receptors are important for intracellular signal transduction, and widely participate in physiological and pathological processes, including pain perception. Group I metabotropic glutamate receptors (mGluRs), including mGluR1 and mGluR5, are predominantly implicated in central sensitization, which can lead to hyperalgesia and allodynia. Many orthosteric site antagonists targeting Group I mGluRs have been found to alleviate NP, but their poor efficacy, low selectivity, and numerous side effects limit their development in NP treatment. Here we reviewed the advantages of Group I mGluRs negative allosteric modulators (NAMs) over orthosteric site antagonists based on allosteric modulation mechanism, and the challenges and opportunities of Group I mGluRs NAMs in NP treatment. This article aims to elucidate the advantages and future development potential of Group I mGluRs NAMs in the treatment of NP.

Interplay of Nav1.8 and Nav1.7 channels drives neuronal hyperexcitability in neuropathic pain

While voltage-gated sodium channels Nav1.7 and Nav1.8 both contribute to electrogenesis in dorsal root ganglion (DRG) neurons, details of their interactions have remained unexplored. Here, we studied the functional contribution of Nav1.8 in DRG neurons using a dynamic clamp to express Nav1.7L848H, a gain-of-function Nav1.7 mutation that causes inherited erythromelalgia (IEM), a human genetic model of neuropathic pain, and demonstrate a profound functional interaction of Nav1.8 with Nav1.7 close to the threshold for AP generation. At the voltage threshold of -21.9 mV, we observed that Nav1.8 channel open-probability exceeded Nav1.7WT channel open-probability ninefold. Using a kinetic model of Nav1.8, we showed that a reduction of Nav1.8 current by even 25-50% increases rheobase and reduces firing probability in small DRG neurons expressing Nav1.7L848H. Nav1.8 subtraction also reduces the amplitudes of subthreshold membrane potential oscillations in these cells. Our results show that within DRG neurons that express peripheral sodium channel Nav1.7, the Nav1.8 channel amplifies excitability at a broad range of membrane voltages with a predominant effect close to the AP voltage threshold, while Nav1.7 plays a major role at voltages closer to resting membrane potential. Our data show that dynamic-clamp reduction of Nav1.8 conductance by 25-50% can reverse hyperexcitability of DRG neurons expressing a gain-of-function Nav1.7 mutation that causes pain in humans and suggests, more generally, that full inhibition of Nav1.8 may not be required for relief of pain due to DRG neuron hyperexcitability.

Cannabis constituents for chronic neuropathic pain; reconciling the clinical and animal evidence

Chronic neuropathic pain is a debilitating pain syndrome caused by damage to the nervous system that is poorly served by current medications. Given these problems, clinical studies have pursued extracts of the plant Cannabis sativa as alternative treatments for this condition. The vast majority of these studies have examined cannabinoids which contain the psychoactive constituent delta-9-tetrahydrocannabinol (THC). While there have been some positive findings, meta-analyses of this clinical work indicates that this effectiveness is limited and hampered by side-effects. This review focuses on how recent preclinical studies have predicted the clinical limitations of THC-containing cannabis extracts, and importantly, point to how they might be improved. This work highlights the importance of targeting channels and receptors other than cannabinoid CB1 receptors which mediate many of the side-effects of cannabis.

Fu's subcutaneous needling promotes axonal regeneration and remyelination by inhibiting inflammation and endoplasmic reticulum stress

Fu's subcutaneous needling (FSN) is a traditional Chinese acupuncture procedure used to treat pain-related neurological disorders. Moreover, the regulation of inflammatory cytokines may provide a favorable environment for peripheral nerve regeneration. In light of this, FSN may be an important novel therapeutic strategy to alleviate pain associated with peripheral neuropathy; however, the underlying molecular mechanisms remain unclear. This study revealed that patients who had osteoarthritis with peripheral neuropathic pain significantly recovered after 1 to 2 weeks of FSN treatment according to the visual analog scale, Western Ontario and McMaster Universities Osteoarthritis Index, Lequesne index, walking speed, and passive range of motion. Similarly, we demonstrated that FSN treatment in an animal model of chronic constriction injury (CCI) significantly improved sciatic nerve pain using paw withdrawal thresholds, sciatic functional index scores, and compound muscle action potential amplitude tests. In addition, transmission electron microscopy images of sciatic nerve tissue showed that FSN effectively reduced axonal swelling, abnormal myelin sheaths, and the number of organelle vacuoles in CCI-induced animals. Mechanistically, RNA sequencing and gene set enrichment analysis revealed significantly reduced inflammatory pathways, neurotransmitters, and endoplasmic reticulum stress pathways and increased nerve regeneration factors in the FSN+CCI group, compared with that in the CCI group. Finally, immunohistochemistry, immunoblotting and enzyme-linked immunosorbent assay showed similar results in the dorsal root ganglia and sciatic nerve. Our findings suggest that FSN can effectively ameliorate peripheral neuropathic pain by regulate inflammation and endoplasmic reticulum stress, thereby determine its beneficial application in patients with peripheral nerve injuries.

Histone modifications and Sp1 promote GPR160 expression in bone cancer pain within rodent models

Bone cancer pain (BCP) affects ~70% of patients in advanced stages, primarily due to bone metastasis, presenting a substantial therapeutic challenge. Here, we profile orphan G protein-coupled receptors in the dorsal root ganglia (DRG) following tumor infiltration, and observe a notable increase in GPR160 expression. Elevated Gpr160 mRNA and protein levels persist from postoperative day 6 for over 18 days in the affected DRG, predominantly in small-diameter C-fiber type neurons specific to the tibia. Targeted interventions, including DRG microinjection of siRNA or AAV delivery, mitigate mechanical allodynia, cold, and heat hyperalgesia induced by the tumor. Tumor infiltration increases DRG neuron excitability in wild-type mice, but not in Gpr160 gene knockout mice. Tumor infiltration results in reduced H3K27me3 and increased H3K27ac modifications, enhanced binding of the transcription activator Sp1 to the Gpr160 gene promoter region, and induction of GPR160 expression. Modulating histone-modifying enzymes effectively alleviated pain behavior. Our study delineates a novel mechanism wherein elevated Sp1 levels facilitate Gpr160 gene transcription in nociceptive DRG neurons during BCP in rodents.

METHA-NeP: effectiveness and safety of methadone for neuropathic pain: a controlled randomized trial

ABSTRACT

In this randomized, double-blind, parallel placebo-controlled clinical trial, we evaluated the efficacy of methadone as an add-on therapy for people with chronic neuropathic pain (NP). Eighty-six patients were randomly assigned to receive methadone or placebo for 8 weeks. The primary outcome was the proportion of participants achieving at least 30% pain relief from baseline using a 100-mm pain Visual Analogue Scale. Secondary outcomes included global impression of change, NP symptoms, sleep quality, quality of life, pain interference in daily activities, and mood. A larger number of responders were found in the methadone (68%), compared to the placebo (33%) arm; risk difference 33.6%; 95% confidence interval 13.0%-54.3%; P = 0.003; number needed to treat = 3.0. Methadone reduced pain intensity ( P < 0.001), burning ( P = 0.023), pressing ( P = 0.005), and paroxysmal dimensions ( P = 0.006) of NP. Methadone also improved sleep ( P < 0.001) and increased the patient's global impression of improvement ( P = 0.002). Methadone did not significantly impact quality of life, pain interference, or mood. Treatment-emergent adverse events occurred in all methadone- and in 73% of placebo-treated patients ( P < 0.001). No serious adverse events or deaths occurred. Discontinuation due to adverse events was reported in 2 participants in the methadone and none in the placebo arm. Methadone use as an add-on to an optimized treatment for NP with first- and/or second-line drugs provided superior analgesia, improved sleep, and enhanced global impression of change, without being associated with significant serious adverse effects that would raise safety concerns.

Beneficial Effects of Ginger Root Extract on Pain Behaviors, Inflammation, and Mitochondrial Function in the Colon and Different Brain Regions of Male and Female Neuropathic Rats: A Gut-Brain Axis Study

BACKGROUND

Neuroinflammation and mitochondrial dysfunction have been implicated in the progression of neuropathic pain (NP) but can be mitigated by supplementation with gingerol-enriched ginger (GEG). However, the exact benefits of GEG for each sex in treating neuroinflammation and mitochondrial homeostasis in different brain regions and the colon remain to be determined.

OBJECTIVE

Evaluate the effects of GEG on emotional/affective pain and spontaneous pain behaviors, neuroinflammation, as well as mitochondria homeostasis in the amygdala, frontal cortex, hippocampus, and colon of male and female rats in the spinal nerve ligation (SNL) NP model.

METHODS

One hundred rats (fifty males and fifty females) were randomly assigned to five groups: sham + vehicle, SNL + vehicle, and SNL with three different GEG doses (200, 400, and 600 mg/kg BW) for 5 weeks. A rat grimace scale and vocalizations were used to assess spontaneous and emotional/affective pain behaviors, respectively. mRNA gene and protein expression levels for tight junction protein, neuroinflammation, mitochondria homeostasis, and oxidative stress were measured in the amygdala, frontal cortex, hippocampus, and colon using qRT-PCR and Western blot (colon).

RESULTS

GEG supplementation mitigated spontaneous pain in both male and female rats with NP while decreasing emotional/affective responses only in male NP rats. GEG supplementation increased intestinal integrity (claudin 3) and suppressed neuroinflammation [glial activation (GFAP, CD11b, IBA1) and inflammation (TNFα, NFκB, IL1β)] in the selected brain regions and colon of male and female NP rats. GEG supplementation improved mitochondrial homeostasis [increased biogenesis (TFAM, PGC1α), increased fission (FIS, DRP1), decreased fusion (MFN2, MFN1) and mitophagy (PINK1), and increased Complex III] in the selected brain regions and colon in both sexes. Some GEG dose-response effects in gene expression were observed in NP rats of both sexes.

CONCLUSIONS

GEG supplementation decreased emotional/affective pain behaviors of males and females via improving gut integrity, suppressing neuroinflammation, and improving mitochondrial homeostasis in the amygdala, frontal cortex, hippocampus, and colon in both male and female SNL rats in an NP model, implicating the gut-brain axis in NP. Sex differences observed in the vocalizations assay may suggest different mechanisms of evoked NP responses in females.

The μ-opioid receptor differentiates two distinct human nociceptive populations relevant to clinical pain

The shortfall in new analgesic agents is a major impediment to reducing reliance on opioid medications for control of severe pain. In both animals and man, attenuating nociceptive transmission from primary afferent neurons with a μ-opioid receptor agonist yields highly effective analgesia. Consequently, deeper molecular characterization of human nociceptive afferents expressing OPRM1, the μ-opioid receptor gene, is a key component for advancing analgesic drug discovery and understanding clinical pain control. A co-expression matrix for the μ-opioid receptor and a variety of nociceptive channels as well as δ- and κ-opioid receptors is established by multiplex in situ hybridization. Our results indicate an OPRM1-positive population with strong molecular resemblance to rodent peptidergic C-nociceptors associated with tissue damage pain and an OPRM1-negative population sharing molecular characteristics of murine non-peptidergic C-nociceptors. The empirical identification of two distinct human nociceptive populations that differ profoundly in their presumed responsiveness to opioids provides an actionable translational framework for human pain control.

Current insights and therapeutic strategies for targeting TRPV1 in neuropathic pain management

Neuropathic pain, a common symptom of several disorders, exerts a substantial socioeconomic burden worldwide. Transient receptor potential vanilloid 1 (TRPV1), a non-selective cation channel predominantly ex-pressed in nociceptive neurons, plays a pivotal role in nociception, by detecting various endogenous and exogenous stimuli, including heat, pro-inflammatory mediators, and physical stressors. Dysregulation of TRPV1 signaling further contributes to the pathophysiology of neuropathic pain. Therefore, targeting TRPV1 is a promising strategy for developing novel analgesics with improved efficacy and safety profiles. Several pharmacological approaches to modulate TRPV1 activity, including agonists, antagonists, and biological TRPV1 RNA interference (RNAi, small interfering RNA [siRNA]) have been explored. Despite preclinical success, the clinical translation of TRPV1-targeted therapies has encountered challenges, including hyperthermia, hypothermia, pungency, and desensitization. Nevertheless, ongoing research efforts aim to refine TRPV1-targeted interventions through structural modifications, development of selective modulators, and discovery of natural, peptide-based drug candidates. Herein, we provide guidance for researchers and clinicians involved in the development of new interventions specifically targeting TRPV1 by reviewing the existing literature and highlighting current research activities. This study further discusses potential future research endeavors for enhancing the efficacy, safety, and tolerability of TRPV1 candidates, and thereby facilitates the translation of these discoveries into effective clinical interventions to alleviate neuropathic pain disorders.

Pharmacologic and Nonpharmacologic Management of Neuropathic Pain

Disorders of the somatosensory nervous system that cause neuropathic pain are treated in a variety of ways. Herein, we introduce a stepwise approach to treating neuropathic pain. We then summarize the available data and guidelines for treating neuropathic pain, both with pharmacologic and nonpharmacologic methods, and provide a synthesized algorithm highlighting the similarities and differences between recent guidelines on the management of neuropathic pain. Pharmacologic treatments are primarily antiseizure medications (e.g., gabapentinoids, sodium channel blockers) and antidepressant medications (e.g., tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors), though other medications and interventional pharmacologic therapies can also be considered. There are a wide variety of nonpharmacologic treatments for neuropathic pain including neuromodulation, nerve stimulation, physiotherapy, movement therapies, lifestyle modification, nutritional supplements, acupuncture, and mind-body techniques.

Pharmacological agents targeting transient receptor potential (TRP) channels in neuropathic pain: Preclinical and clinical status

Neuropathic pain generally affects 7-10% population worldwide and an estimated ∼1 in every 20 individuals in western countries suffer and burden to society. The most limiting factor with existing therapies includes dose escalation issues, off-target side effects and poor translation of randomized trials into clinical practice. Neuropathic pain is a broad term that comprises direct injury/damage to the central and/or peripheral nervous system, leads to maladaptive changes in neuronal as well as in non-neuronal cells, which further contributes to the spontaneous pain, sensory and motor deficit along with altered sensitivity towards the noxious as well as non-noxious stimulus. Transient receptor potential (TRP) channels are polymodal, non-specific cation channels that operate as biosensors to various mechanical and chemical stimuli, including hyperosmolarity, shear stress, heat, mechanical stretch, extracellular ATP, and other products of inflammation. Modulation of these channels leads to various physiological and pathophysiological manifestations at molecular and cellular levels, leading to diseases including neuropathic pain. There are several molecules targeting TRP channels for neuropathic pain in pre-clinical studies, clinical trials and in the market. This review highlights the critical involvement of various pharmacological modulators for TRP channels targeting neuropathic pain and their possible outcomes to harness the therapeutic potential of TRP channels.

Evaluation of somatosensory bedside testing and neurodynamics of the trigeminal nerve in craniofacial pain: A matched case-control study

OBJECTIVE

The objective of this study was to investigate whether trigeminal somatosensory function and mechanosensitivity differ between groups with craniofacial neuropathic pain (CNP), non-neuropathic craniofacial pain (NNP), and healthy controls (HC).

METHODS

Thirty-three participants were categorized into these groups, matched for age and sex. The study evaluated pain intensity, the Leeds Assessment of Neuropathic Symptoms and Signs (LANSS), and various trigeminal somatosensory tests, including vibration, pressure pain, thermal detection, cold pain, and neurodynamic tests of the trigeminal nerve.

RESULTS

Cold pain thresholds differed significantly among the three groups CNP, NNP, and HC (p = .047). No difference was found in vibration detection, pressure pain threshold, and thermal detection. Trigeminal nerve mechanosensitivity was significantly different among the three groups (p = .03), particularly between groups CNP and HC (p = .01).

CONCLUSION

Differences in aspects of trigeminal somatosensory function, including cold pain and trigeminal mechanosensitivity, exist between subjects with chronic craniofacial pain and HC. This implies that a clinical classification system for neuromusculoskeletal rehabilitation could be valuable in evaluating patients.

To Be in Pain: Pain Multidimensional Questionnaire as Reliable Tool to Evaluate Multifaceted Aspects of Pain

Background/Objectives: Pain is a multidimensional experience influenced by sensory, emotional, and cognitive factors. Traditional pain assessments often fail to capture this complexity. This study aimed to develop and validate the Pain Multidimensional Questionnaire (Pa-M-QU), a new self-report tool designed to assess pain catastrophizing, sensitivity, and coping strategies. Methods: Two independent samples of Italian-speaking participants, aged 18 and above, were recruited online. The first sample (n = 392; mean age = 29.36) was used for exploratory factor analysis (EFA), and the second sample (n = 123; mean age = 28.0) for confirmatory factor analysis (CFA). Pearson's correlations and convergent validity analyses were conducted. Results: From an initial pool of 59 items identified through focus group discussions, 35 items were removed based on reliability analysis. The final 24-item Pa-M-QU features a three-factor structure: catastrophizing, pain sensitivity, and coping with pain. Conclusions: The Pa-M-QU offers a rapid, non-invasive assessment that captures the multidimensional nature of pain. It is a starting point to develop tools for both clinical and research settings, aiding in evaluating pain in healthy individuals and predicting acute and chronic pain disorders. Future research should focus on refining the Pa-M-QU for broader clinical applications and exploring its potential to complement or replace traditional pain assessments, thereby advancing pain management and research.

Nicorandil antiallodynic activity in a model of neuropathic pain is associated with the activation of ATP-dependent potassium channels and opioidergic pathways, and reduced production of cytokines and neutrophils recruitment in paw, sciatic nerve, and dorsal root ganglia

BACKGROUND

Recently, we demonstrated that nicorandil inhibits mechanical allodynia induced by paclitaxel. In the present study, we evaluated the effect induced by nicorandil in a model of neuropathic pain induced by chronic constriction injury (CCI) in mice. We also investigated putative mechanisms underlying such an effect.

METHODS

CCI was induced by three ligatures of the left sciatic nerve. Mechanical allodynia was evaluated by measuring the paw withdrawal threshold with an electronic von Frey apparatus. Concentrations of cytokines and myeloperoxidase activity were determined in the paw tissue, sciatic nerve, and dorsal root ganglia (DRG).

RESULTS

Oral administration of two doses of nicorandil (150 mg/kg po), but not equimolar doses of nicotinamide or nicotinic acid, attenuated mechanical allodynia induced by CCI. Nicorandil activity was reduced by previous administration of glibenclamide (40 mg/kg) or naltrexone (5 mg/kg or 10 mg/kg). Two doses of nicorandil (150 mg/kg, po) reduced tumor necrosis factor-α, interleukin-1β and interleukin-6, but not CXCL-1, concentrations in the paw tissue of CCI mice. Two doses of nicorandil (150 mg/kg, po) reduced concentrations of all these mediators in the sciatic nerve and DRG. Two doses of nicorandil (150 mg/kg, po) also reduced the myeloperoxidase activity in the paw tissue, sciatic nerve, and DRG.

CONCLUSIONS

Nicorandil exhibits antiallodynic activity in a model of neuropathic pain induced by CCI. Inhibition of cytokines production and reduction of neutrophils recruitment in paw tissue, sciatic nerve, and DRG as well as activation of ATP-dependent potassium channels and opioidergic pathways, underlie nicorandil antiallodynic activity.

Analgesic candidate adenosine A 3 receptors are expressed by perineuronal peripheral macrophages in human dorsal root ganglion and spinal cord microglia

ABSTRACT

Adenosine receptors are a family of purinergic G protein-coupled receptors that are widely distributed in bodily organs and in the peripheral and central nervous systems. Recently, antihyperalgesic actions have been suggested for the adenosine A 3 receptor, and its agonists have been proposed as new neuropathic pain treatments. We hypothesized that these receptors may be expressed in nociceptive primary afferent neurons. However, RNA sequencing across species, eg, rat, mouse, dog, and human, suggests that dorsal root ganglion (DRG) expression of ADORA3 is inconsistent. In rat and mouse, Adora3 shows very weak to no expression in DRG, whereas it is well expressed in human DRG. However, the cell types in human DRG that express ADORA3 have not been delineated. An examination of DRG cell types using in situ hybridization clearly detected ADORA3 transcripts in peripheral macrophages that are in close apposition to the neuronal perikarya but not in peripheral sensory neurons. By contrast, ADORA1 was found primarily in neurons, where it is broadly expressed at low levels. These results suggest that a more complex or indirect mechanism involving modulation of macrophage and/or microglial cells may underlie the potential analgesic action of adenosine A 3 receptor agonism.

CARTp/GPR160 mediates behavioral hypersensitivities in mice through NOD2

ABSTRACT

Neuropathic pain is a debilitating chronic condition that remains difficult to treat. More efficacious and safer therapeutics are needed. A potential target for therapeutic intervention recently identified by our group is the G-protein coupled receptor 160 (GPR160) and the cocaine- and amphetamine-regulated transcript peptide (CARTp) as a ligand for GPR160. Intrathecal administration of CARTp in rodents causes GPR160-dependent behavioral hypersensitivities. However, the molecular and biochemical mechanisms underpinning GPR160/CARTp-induced behavioral hypersensitivities in the spinal cord remain poorly understood. Therefore, we performed an unbiased RNA transcriptomics screen of dorsal horn spinal cord (DH-SC) tissues harvested at the time of peak CARTp-induced hypersensitivities and identified nucleotide-binding oligomerization domain-containing protein 2 (Nod2) as a gene that is significantly upregulated. Nucleotide-binding oligomerization domain-containing protein 2 is a cytosolic pattern-recognition receptor involved in activating the immune system in response to bacterial pathogens. While NOD2 is well studied under pathogenic conditions, the role of NOD2-mediated responses in nonpathogenic settings is still not well characterized. Genetic and pharmacological approaches reveal that CARTp-induced behavioral hypersensitivities are driven by NOD2, with co-immunoprecipitation studies indicating an interaction between GPR160 and NOD2. Cocaine- and amphetamine-regulated transcript peptide-induced behavioral hypersensitivities are independent of receptor-interacting protein kinase 2 (RIPK2), a common adaptor protein to NOD2. Immunofluorescence studies found NOD2 co-expressed with endothelial cells rather than glial cells, implicating potential roles for CARTp/NOD2 signaling in these cells. While these findings are based only on studies with male mice, our results identify a novel pathway by which CARTp causes behavioral hypersensitivities in the DH-SC through NOD2 and highlights the importance of NOD2-mediated responses in nonpathogenic settings.

Positive sensory symptoms, in surgically managed patients with carpal tunnel syndrome: A long term follow‑up

Carpal tunnel syndrome (CTS) is the most frequent entrapment neuropathy. Patients commonly experience neuropathic pain, leading them to seek medical advice. However, other symptoms experienced in patients with CTS, such as paresthesia, dysesthesia and allodynia, classed as positive sensory symptoms (PSS), are often under-reported. In the present study, patients with surgically-managed CTS were observed pre- and post-surgery to evaluate PSS, using the symptoms scale component of the Boston Carpal Tunnel Questionnaire (BCTQ) and the Sensory Frequency of Symptoms Scale. In total, 19 patients were included in the present study, with 79% female patients, and a mean age of 54±10.59 years. In addition, the mean follow-up was 63±29.91 months. The results of the present study revealed a pre-surgery BCTQ score of 3.52±0.63 and a post-surgery BCTQ score of 1.58±0.61. Notably, improvements in pain were observed, at 7.7±2.26 pre-surgery compared with 1.65±2.88 post-surgery. Compared with pre-surgery, post-surgery paresthesia scores were reduced from 2.94±0.82 to 0.47±0.45, dysesthesia scores were reduced from 2.52±0.84 to 0.47±0.39 and allodynia scores were reduced from 0.63±0.75 to 0.26±0.47. In conclusion, the results of the present study demonstrated that median nerve decompression ameliorated CTS symptoms, such as paresthesia and dysesthesia. However, further investigations are required to verify the benefits of surgery in relieving allodynia.

Transcriptional reprogramming post-peripheral nerve injury: A systematic review

Neuropathic pain is characterised by periodic or continuous hyperalgesia, numbness, or allodynia, and results from insults to the somatosensory nervous system. Peripheral nerve injury induces transcriptional reprogramming in peripheral sensory neurons, contributing to increased spinal nociceptive input and the development of neuropathic pain. Effective treatment for neuropathic pain remains an unmet medical need as current therapeutics offer limited effectiveness and have undesirable effects. Understanding transcriptional changes in peripheral nerve injury-induced neuropathy might offer a path for novel analgesics. Our literature search identified 65 papers exploring transcriptomic changes post-peripheral nerve injury, many of which were conducted in animal models. We scrutinize their transcriptional changes data and conduct gene ontology enrichment analysis to reveal their common functional profile. Focusing on genes involved in 'sensory perception of pain' (GO:0019233), we identified transcriptional changes for different ion channels, receptors, and neurotransmitters, shedding light on its role in nociception. Examining peripheral sensory neurons subtype-specific transcriptional reprograming and regeneration-associated genes, we delved into downstream regulation of hypersensitivity. Identifying the temporal program of transcription regulatory mechanisms might help develop better therapeutics to target them effectively and selectively, thus preventing the development of neuropathic pain without affecting other physiological functions.

Spared ulnar nerve injury results in increased layer III-VI excitability in the pig somatosensory cortex

This study describes cortical recordings in a large animal nerve injury model. We investigated differences in primary somatosensory cortex (S1) hyperexcitability when stimulating injured and uninjured nerves and how different cortical layers contribute to S1 hyperexcitability after spared ulnar nerve injury. We used a multielectrode array to record single-neuron activity in the S1 of ten female Danish landrace pigs. Electrical stimulation of the injured and uninjured nerve evoked brain activity up to 3 h after injury. The peak amplitude and latency of early and late peristimulus time histogram responses were extracted for statistical analysis. Histological investigations determined the layer of the cortex in which each electrode contact was placed. Nerve injury increased the early peak amplitude compared with that of the control group. This difference was significant immediately after nerve injury when the uninjured nerve was stimulated, while it was delayed for the injured nerve. The amplitude of the early peak was increased in layers III-VI after nerve injury compared with the control. In layer III, S1 excitability was also increased compared with preinjury for the early peak. Furthermore, the late peak was significantly larger in layer III than in the other layers in the intervention and control group before and after injury. Thus, the most prominent increase in excitability occurred in layer III, which is responsible for the gain modulation of cortical output through layer V. Therefore, layer III neurons seem to have an important role in altered brain excitability after nerve injury.

Principles of Pain Management

OBJECTIVE

This article introduces the general principles of assessing, diagnosing, and managing pain relevant to neurologic practice.

LATEST DEVELOPMENTS

Scientific understanding of and clinical practices related to pain and pain management are advancing. The field is remarkable for the diversity of health professions engaged in this effort, including physicians, scientists, psychologists, pharmacists, and many others. Pain classification is transforming with pending changes to the International Classification of Diseases diagnostic coding system, and pain assessment has moved toward consistent application of the biopsychosocial model. The diagnosis of pain has continued to become more sophisticated with the development of additional testing modalities, clearer classification systems, and diagnostic criteria. Pain management requires both pharmacologic and nonpharmacologic elements; systematic review evidence for both of these and interventional and surgical management are increasingly available. The context of treatment remains important given the impact of social determinants of health and limitations of access to diagnostic and treatment resources. Due to global and interprofessional collaborations as well as new research funding, the outlook is positive.

ESSENTIAL POINTS

Pain is a protean experience for humans; functional MRI (fMRI) and other research modalities show that pain perception is highly multifocal, and modulation occurs at many nervous system levels. Neurologists bring special skills to pain evaluation and management, are well equipped to appreciate both the focal and diffuse nature of pain, and can envision how pain attenuates sleep, cognitive function, mobility, motivation, and social connection. By operationalizing expert knowledge of the nervous system, implementing relevant therapies, and collaborating with diverse health professions to manage pain, neurologists can succeed at and find meaning in optimizing patient outcomes.

Down-regulation of microRNA-382-5p reduces neuropathic pain by targeting regulation of dual specificity phosphatase-1

Background

MicroRNA (miRNA) plays a crucial role in neuropathic pain (NP) by targeting mRNAs. This study aims to analyze the regulatory function and mechanism of miR-382-5p/dual specificity phosphatase-1 (DUSP1) axis in NP.

Methods

We utilized rats with chronic constriction injury (CCI) of the sciatic nerve as the NP model. The levels of miR-382-5p and DUSP1 were reduced by intrathecal injection of lentiviral interference vectors targeting miR-382-5p and DUSP1. The mRNA levels of miR-382-5p and DUSP1 in the dorsal root ganglions (DRGs) were measured by RT-qPCR assay. The pain behavior was evaluated by mechanical nociceptive sensitivity and thermal nociceptive sensitivity. The expression levels of interleukin-6 (IL)-6, IL-1β, and tumor necrosis factor-α in the DRGs were analyzed by ELISA assay. The targeting relationship between miR-382-5p and DUSP1 was verified by DLR assay and RIP assay.

Results

Compared to the Sham group, the CCI rats exhibited higher levels of miR-382-5p and lower levels of DUSP1. Overexpression of miR-382-5p significantly decreased DUSP1 levels. Reducing miR-382-5p levels can lower the mechanical nociceptive sensitivity and thermal nociceptive sensitivity of CCI rats and inhibit the over-activation of pro-inflammatory factors. Reduced miR-382-5p levels decreased NP in CCI rats. DUSP1 is the target of miR-382-5p, and down-regulation of DUSP1 reverses the inhibitory effect of reduced miR-382-5p levels on NP.

Conclusions

Down-regulation of miR-382-5p inhibits the over-activation of pro-inflammatory factors by targeting and regulating the expression of DUPS1, thereby alleviating NP.

Nicotinamide riboside activates SIRT3 to prevent paclitaxel-induced peripheral neuropathy

Paclitaxel (PTX) is a microtubule stabilizer that disrupts the normal cycle of microtubule depolymerization and repolymerization, leading to cell cycle arrest and cancer cell death. It is commonly used as a first-line chemotherapeutics for various malignancies, such as breast cancer, non-small cell lung cancer, and ovarian cancer. However, PTX chemotherapy is associated with common and serious side effects, including chemotherapy-induced peripheral neuropathy (CIPN). As cancer treatment advances and survival rates increase, the impact of CIPN on patients' quality of life has become more significant. To date, there is no effective treatment strategy for CIPN. Surtuin3 (SIRT3) is a nicotinamide adenine dinucleotide (NAD+) dependent protein deacetylase located on mitochondria. It transfers the acetyl group of the lysine side chain of acetylated substrate proteins to NAD+, producing deacetylated proteins to regulate mitochondrial energy metabolic processes. SIRT3 has been found to play an important role in various diseases, including aging, neurodegenerative diseases, cancer, heart disease, metabolic diseases, etc. However, the role of SIRT3 in CIPN is still unknown. This study found for the first time that activating SIRT3 helps to improve paclitaxel-induced CIPN. Nicotinamide riboside (NR) can protect dorsal root ganglion (DRG) mitochondria against oxidative damage caused by paclitaxel through activating SIRT3-MnSOD2 and SIRT3-Nrf2 pathway. Moreover, NR can enhance the anticancer activity of paclitaxel. Together, our research provides new strategy and candidate drug for the treatment of CIPN.

Genetically predicted immune cells mediate the association between gut microbiota and neuropathy pain

BACKGROUND

Previous observational studies have indicated a complex association between gut microbiota (GM) and neuropathic pain (NP). Nonetheless, the precise biological mechanisms underlying this association remain unclear. Therefore, we adopted a Mendelian randomization (MR) approach to investigate the causal relationship between GM and neuropathic pain including post-herpetic neuralgia (PHN), painful diabetic peripheral neuropathy (PDPN), and trigeminal neuralgia (TN), as well as to explore the potential mediation effects of immune cells.

METHODS

We performed a two-step, two-sample Mendelian randomization study with an inverse variance-weighted (IVW) approach to investigate the causal role of GM on three major kinds of NP and the mediation effect of immune cells between the association of GM and NP. In addition, we determine the strongest causal associations using Bayesian weighted Mendelian randomization (BWMR) analysis. Furthermore, we will investigate the mediating role of immune cells through a two-step Mendelian randomization design.

RESULTS

We identified 53 taxonomies and pathways of gut microbiota that had significant causal associations with NP. In addition, we also discovered 120 immune cells that exhibited significant causal associations with NP. According to the BWMR and two-step Mendelian randomization analysis, we identified the following results CD4 on CM CD4 + (maturation stages of T cell) mediated 6.7% of the risk reduction for PHN through the pathway of fucose degradation (FUCCAT.PWY). CD28 + DN (CD4-CD8-) AC (Treg) mediated 12.5% of the risk reduction for PHN through the influence on Roseburia inulinivorans. CD45 on lymphocyte (Myeloid cell) mediated 11.9% of the risk increase for TN through the superpathway of acetyl-CoA biosynthesis (PWY.5173). HLA DR + CD8br %T cell (TBNK) mediated 3.2% of the risk reduction for TN through the superpathway of GDP-mannose-derived O-antigen building blocks biosynthesis (PWY.7323). IgD-CD38-AC (B cell) mediated 7.5% of the risk reduction for DPN through the pathway of thiazole biosynthesis I in E. coli (PWY.6892).

DISCUSSION

These findings provided evidence supporting the causal effect of GM with NP, with immune cells playing a mediating role. These findings may inform prevention strategies and interventions directed toward NP. Future studies should explore other plausible biological mechanisms.

Therapeutic Efficacy of Adipose Tissue-Derived Components in Neuropathic Pain: A Systematic Review

BACKGROUND

Neuropathic pain results from a defect in the somatosensory nervous system caused by a diversity of etiologies. The effect of current treat-ment with analgesics and surgery is limited. Studies report the therapeutic use of adipose tissue-derived components to treat neuropathic pain as a new treatment modality.

OBJECTIVE

The aim of this systematic review was to investigate the therapeutic clinical efficacy of adipose tissue-derived components on neuro-pathic pain.

METHODS

PubMed, Medline, Cochrane and Embase databases were searched until August 2023. Clinical studies assessing neuropathic pain after autologous fat grafting or the therapeutic use of adipose tissue-derived com-ponents were included. The outcomes of interest were neuropathic pain and quality of life.

RESULTS

In total, 433 studies were identified, of which 109 dupli-cates were removed, 324 abstracts were screened and 314 articles were excluded. In total, ten studies were included for comparison. Fat grafting and cellular stromal vascular fraction were used as treatments. Fat grafting indications were post-mastectomy pain syndrome, neuromas, post-herpetic neuropathy, neuro-pathic scar pain and trigeminal neuropathic pain. In seven studies, neuropathic pain levels decreased, and overall, quality of life did not improve.

CONCLUSIONS

The therapeutic efficacy of adipose tissue-derived components in the treatment of neuropathic pain remains unclear due to the few performed clinical trials with small sample sizes for various indications. Larger and properly designed (randomized) controlled trials are required.

Peripheral Nerve Stimulation for Neuropathic Pain Management: A Narrative Review

This narrative review examines the therapeutic efficacy of peripheral nerve stimulation (PNS) in the treatment of neuropathic pain (NP), a type of pain arising from lesions or diseases of the somatosensory system with a global prevalence ranging from 6.90% to 10.00%. Traditional pharmacological interventions often fall short for many persons, highlighting the need for alternative treatments such as PNS, which has demonstrated significant promise with minimal side effects. The review summarizes the effectiveness of PNS in various NP conditions, including trigeminal neuralgia and postherpetic neuralgia, and underscores the need for further research to refine treatment approaches. The mechanism of PNS is discussed, involving the activation of non-nociceptive Aβ fibers and modulation of neurotransmitters, and offering pain relief through both peripheral and central pathways. Despite the proven efficacy of PNS, challenges remain, including the need for randomized controlled trials and the optimization of stimulation parameters. The review concludes that PNS is a promising treatment modality for NP, warranting additional high-quality trials to solidify its role in clinical practice.

The mechanism and potential therapeutic target of piezo channels in pain

Pain is a common symptom of many clinical diseases; it adversely affects patients' physical and mental health, reduces their quality of life, and heavily burdens patients and society. Pain treatment is one of the most difficult problems today. There is an urgent need to explore the potential factors involved in the pathogenesis of pain to improve its diagnosis and treatment rate. Piezo1/2, a newly identified mechanosensitive ion channel opens in response to mechanical stimuli and plays a critical role in regulating pain-related diseases. Inhibition or downregulation of Piezo1/2 alleviates disease-induced pain. Therefore, in this study, we comprehensively discussed the biology of this gene, focusing on its potential relevance in pain-related diseases, and explored the pharmacological effects of drugs using this gene for the treatment of pain.

Thin-film implants for bioelectronic medicine

This article is based on the MRS Mid-Career Researcher Award "for outstanding contributions to the fundamentals and development of organic electronic materials and their application in biology and medicine" presentation given by George G. Malliaras, University of Cambridge, at the 2023 MRS Spring Meeting in San Francisco, Calif.Bioelectronic medicine offers a revolutionary approach to treating disease by stimulating the body with electricity. While current devices show safety and efficacy, limitations, including bulkiness, invasiveness, and scalability, hinder their wider application. Thin-film implants promise to overcome these limitations. Made using microfabrication technologies, these implants conform better to neural tissues, reduce tissue damage and foreign body response, and provide high-density, multimodal interfaces with the body. This article explores how thin-film implants using organic materials and novel designs may contribute to disease management, intraoperative monitoring, and brain mapping applications. Additionally, the technical challenges to be addressed for this technology to succeed are discussed.

Graphical abstract

B cells drive neuropathic pain-related behaviors in mice through IgG-Fc gamma receptor signaling

Neuroimmune interactions are essential for the development of neuropathic pain, yet the contributions of distinct immune cell populations have not been fully unraveled. Here, we demonstrate the critical role of B cells in promoting mechanical hypersensitivity (allodynia) after peripheral nerve injury in male and female mice. Depletion of B cells with a single injection of anti-CD20 monoclonal antibody at the time of injury prevented the development of allodynia. B cell-deficient (muMT) mice were similarly spared from allodynia. Nerve injury was associated with increased immunoglobulin G (IgG) accumulation in ipsilateral lumbar dorsal root ganglia (DRGs) and dorsal spinal cords. IgG was colocalized with sensory neurons and macrophages in DRGs and microglia in spinal cords. IgG also accumulated in DRG samples from human donors with chronic pain, colocalizing with a marker for macrophages and satellite glia. RNA sequencing revealed a B cell population in naive mouse and human DRGs. A B cell transcriptional signature was enriched in DRGs from human donors with neuropathic pain. Passive transfer of IgG from injured mice induced allodynia in injured muMT recipient mice. The pronociceptive effects of IgG are likely mediated through immune complexes interacting with Fc gamma receptors (FcγRs) expressed by sensory neurons, microglia, and macrophages, given that both mechanical allodynia and hyperexcitability of dissociated DRG neurons were abolished in nerve-injured FcγR-deficient mice. Consistently, the pronociceptive effects of IgG passive transfer were lost in FcγR-deficient mice. These data reveal that a B cell-IgG-FcγR axis is required for the development of neuropathic pain in mice.

Cells and circuits for amygdala neuroplasticity in the transition to chronic pain

Maladaptive plasticity is linked to the chronification of diseases such as pain, but the transition from acute to chronic pain is not well understood mechanistically. Neuroplasticity in the central nucleus of the amygdala (CeA) has emerged as a mechanism for sensory and emotional-affective aspects of injury-induced pain, although evidence comes from studies conducted almost exclusively in acute pain conditions and agnostic to cell type specificity. Here, we report time-dependent changes in genetically distinct and projection-specific CeA neurons in neuropathic pain. Hyperexcitability of CRF projection neurons and synaptic plasticity of parabrachial (PB) input at the acute stage shifted to hyperexcitability without synaptic plasticity in non-CRF neurons at the chronic phase. Accordingly, chemogenetic inhibition of the PB→CeA pathway mitigated pain-related behaviors in acute, but not chronic, neuropathic pain. Cell-type-specific temporal changes in neuroplasticity provide neurobiological evidence for the clinical observation that chronic pain is not simply the prolonged persistence of acute pain.

Role of Exercise on Neuropathic Pain in Preclinical Models: Perspectives for Neuroglia

The benefits of exercise on neuropathic pain (NP) have been demonstrated in numerous studies. In recent studies, inflammation, neurotrophins, neurotransmitters, and endogenous opioids are considered as the main mechanisms. However, the role of exercise in alleviating NP remains unclear. Neuroglia, widely distributed in both the central and peripheral nervous systems, perform functions such as support, repair, immune response, and maintenance of normal neuronal activity. A large number of studies have shown that neuroglia play an important role in the occurrence and development of NP, and exercise can alleviate NP by regulating neuroglia. This article reviewed the involvement of neuroglia in the development of NP and their role in the exercise treatment of NP, intending to provide a theoretical basis for the exercise treatment strategy of NP.

Transcriptome analysis unveils PLSCR1 associated with microglial polarization in neuropathic pain

Neuropathic pain (NP) continues to be a significant problem that lacks effective treatment. Our study sought to explore a new promising gene target for the treatment of NP. Differential and enrichment analyses were performed on 24,197 genes and 12,088 genes from the NP microglial microarray and sequencing dataset. Candidate differentially expressed genes (DEGs), functions, and signaling pathways that are closely related to NP were identified by analyzing the bioinformatic results. For in vivo experiments, mice were divided into the sham and NP groups. The expressions of DEGs were validated to screen out the NP hub genes. For in vitro experiments, the hub genes in resting M0-BV2 and polarized M1-BV2 microglia were examined by immunofluorescence, flow cytometry, and qRT-PCR. DEGs in the NP microarray and sequencing data shared five candidate genes, CD244, MEGF9, PCGF2, PLSCR1, and NECAB2. The results of the in vivo experiment showed that the NP model group exhibited higher expression of PLSCR1 and MEGF9 compared to the sham group. The enrichment results of the DEGs revealed the biological processes of "response to lipopolysaccharide". PLSCR1 was highly expressed in the lipopolysaccharide-induced M1-BV2 microglia. PLSCR1 is a potential gene associated with microglial polarization in NP. These findings provide a new view on understanding the pathogenesis mechanism of NP.

Membrane Lipid Nanodomains Modulate HCN Pacemaker Channels in Nociceptor DRG Neurons

Cell membranes consist of heterogeneous lipid nanodomains that influence key cellular processes. Using FRET-based fluorescent assays and fluorescence lifetime imaging microscopy (FLIM), we found that the dimension of cholesterol-enriched ordered membrane domains (OMD) varies considerably, depending on specific cell types. Particularly, nociceptor dorsal root ganglion (DRG) neurons exhibit large OMDs. Disruption of OMDs potentiated action potential firing in nociceptor DRG neurons and facilitated the opening of native hyperpolarization-activated cyclic nucleotide-gated (HCN) pacemaker channels. This increased neuronal firing is partially due to an increased open probability and altered gating kinetics of HCN channels. The gating effect on HCN channels was likely due to a direct modulation of their voltage sensors by OMDs. In animal models of neuropathic pain, we observed reduced OMD size and a loss of HCN channel localization within OMDs. Additionally, cholesterol supplementation inhibited HCN channels and reduced neuronal hyperexcitability in pain models. These findings suggest that disturbances in lipid nanodomains play a critical role in regulating HCN channels within nociceptor DRG neurons, influencing pain modulation.

Photoswitchable Carbamazepine Analogs for Non-Invasive Neuroinhibition In Vivo

A problem of systemic pharmacotherapy is off-target activity, which causes adverse effects. Outstanding examples include neuroinhibitory medications like antiseizure drugs, which are used against epilepsy and neuropathic pain but cause systemic side effects. There is a need of drugs that inhibit nerve signals locally and on-demand without affecting other regions of the body. Photopharmacology aims to address this problem with light-activated drugs and localized illumination in the target organ. Here, we have developed photoswitchable derivatives of the widely prescribed antiseizure drug carbamazepine. For that purpose, we expanded our method of ortho azologization of tricyclic drugs to meta/para and to N-bridged diazocine. Our results validate the concept of ortho cryptoazologs (uniquely exemplified by Carbazopine-1) and bring to light Carbadiazocine (8), which can be photoswitched between 400-590 nm light (using violet LEDs and halogen lamps) and shows good drug-likeness and predicted safety. Both compounds display photoswitchable activity in vitro and in translucent zebrafish larvae. Carbadiazocine (8) also offers in vivo analgesic efficacy (mechanical and thermal stimuli) in a rat model of neuropathic pain and a simple and compelling treatment demonstration with non-invasive illumination.

SUMOylation and DeSUMOylation: Tug of War of Pain Signaling

SUMOylation is a post-translational modification that attaches a small ubiquitin-like modifier (SUMO) group to a target protein via SUMO ligases, while deSUMOylation refers to the removal of this SUMO group by sentrin-specific proteases (SENPs). Although the functions of these processes have been well described in the nucleus, the role of SUMOylation and deSUMOylation in regulating ion channels is emerging as a novel area of study. Despite this, their contributions to pain signaling remain less clear. Therefore, this review consolidates the current evidence on the link(s) between SUMOylation, deSUMOylation, and pain, with a specific focus on ion channels expressed in the sensory system. Additionally, we explore the role of SUMOylation in the expression and function of kinases, vesicle proteins, and transcription factors, which result in the modulation of certain ion channels contributing to pain. Altogether, this review aims to highlight the relationship between SUMOylation and deSUMOylation in the modulation of ion channels, ultimately exploring the potential therapeutic role of these processes in chronic pain.

Molecular mechanisms of Schisandra chinensis in treating depression-neuropathic pain comorbidity by network pharmacology and molecular docking analysis

This study utilized network pharmacology and docking analyses to explore a groundbreaking therapeutic approach for managing the neuropathic pain and depressive disorder (NP/DD) comorbidity. Schisandra chinensis (SC), a common Chinese medicine, has demonstrated numerous beneficial effects in treating neuropsychological disorders. The main objective of this study was to identify potential bioactive components of SC and investigate their interactions with relevant target genes associated with NP/DD. To gain insights into the underlying molecular mechanisms, GO and KEGG analyses were conducted. Furthermore, molecular docking analysis was employed to validate the therapeutic relevance of SC's active ingredients. Seven bioactive components of SC, namely Longikaurin A, Deoxyharringtonine, Angeloylgomisin O, Schisandrin B, Gomisin A, Gomisin G, and Gomisin R, exhibited effectiveness in the treatment of NP/DD. From this list, the first five components were selected for further analysis. The analyses revealed a complex network of interactions between the targets of SC and NP/DD, providing valuable information about the molecular mechanisms involved in the treatment of NP/DD with SC. SC components demonstrated the ability to regulate pathways involving tumor necrosis factor (TNF), vascular endothelial growth factor (VEGF), and other growth hormones (GH). Overall, this study contributes to our understanding of the molecular mechanisms underlying the effects of SC in treating NP/DD. Further investigation is necessary to explore the therapeutic potential of SC as a viable strategy for NP/DD comorbidity. These findings lay a solid foundation for future research endeavors in this field, holding potential implications for the development of novel therapeutic interventions targeting NP/DD.

The dual role of TRPV1 in peripheral neuropathic pain: pain switches caused by its sensitization or desensitization

The transient receptor potential vanilloid 1 (TRPV1) channel plays a dual role in peripheral neuropathic pain (NeuP) by acting as a "pain switch" through its sensitization and desensitization. Hyperalgesia, commonly resulting from tissue injury or inflammation, involves the sensitization of TRPV1 channels, which modulates sensory transmission from primary afferent nociceptors to spinal dorsal horn neurons. In chemotherapy-induced peripheral neuropathy (CIPN), TRPV1 is implicated in neuropathic pain mechanisms due to its interaction with ion channels, neurotransmitter signaling, and oxidative stress. Sensitization of TRPV1 in dorsal root ganglion neurons contributes to CIPN development, and inhibition of TRPV1 channels can reduce chemotherapy-induced mechanical hypersensitivity. In diabetic peripheral neuropathy (DPN), TRPV1 is involved in pain modulation through pathways including reactive oxygen species and cytokine production. TRPV1's interaction with TRPA1 channels further influences chronic pain onset and progression. Therapeutically, capsaicin, a TRPV1 agonist, can induce analgesia through receptor desensitization, while TRPV1 antagonists and siRNA targeting TRPV1 show promise in preclinical studies. Cannabinoid modulation of TRPV1 provides another potential pathway for alleviating neuropathic pain. This review summarizes recent preclinical research on TRPV1 in association with peripheral NeuP.

Current Treatment Methods for Charcot-Marie-Tooth Diseases

Charcot-Marie-Tooth (CMT) disease, the most common inherited neuromuscular disorder, exhibits a wide phenotypic range, genetic heterogeneity, and a variable disease course. The diverse molecular genetic mechanisms of CMT were discovered over the past three decades with the development of molecular biology and gene sequencing technologies. These methods have brought new options for CMT reclassification and led to an exciting era of treatment target discovery for this incurable disease. Currently, there are no approved disease management methods that can fully cure patients with CMT, and rehabilitation, orthotics, and surgery are the only available treatments to ameliorate symptoms. Considerable research attention has been given to disease-modifying therapies, including gene silencing, gene addition, and gene editing, but most treatments that reach clinical trials are drug treatments, while currently, only gene therapies for CMT2S have reached the clinical trial stage. In this review, we highlight the pathogenic mechanisms and therapeutic investigations of different subtypes of CMT, and promising therapeutic approaches are also discussed.

Discovery and Profiling of New Multimodal Phenylglycinamide Derivatives as Potent Antiseizure and Antinociceptive Drug Candidates

We developed a focused series of original phenyl-glycinamide derivatives which showed potent activity across in vivo mouse seizure models, namely, maximal electroshock (MES) and 6 Hz (using both 32 and 44 mA current intensities) seizure models. Following intraperitoneal (i.p.) administration, compound (R)-32, which was identified as a lead molecule, demonstrated potent protection against all seizure models with ED50 values of 73.9 mg/kg (MES test), 18.8 mg/kg (6 Hz, 32 mA test), and 26.5 mg/kg (6 Hz, 44 mA test). Furthermore, (R)-32 demonstrated efficacy in both the PTZ-induced kindling paradigm and the ivPTZ seizure threshold test. The expression of neurotrophic factors, such as mature brain-derived neurotrophic factor (mBDNF) and nerve growth factor (NGF), in the hippocampus and/or cortex of mice, and the levels of glutamate and GABA were normalized after PTZ-induced kindling by (R)-32. Importantly, besides antiseizure activity, (R)-32 demonstrated potent antinociceptive efficacy in formalin-induced pain, capsaicin-induced pain, as well as oxaliplatin- and streptozotocin-induced peripheral neuropathy in mice (i.p.). No influence on muscular strength and body temperature in mice was observed. Pharmacokinetic studies and in vitro ADME-Tox data (i.e., high metabolic stability in human liver microsomes, a weak influence on CYPs, no hepatotoxicity, satisfactory passive transport, etc.) proved favorable drug-like properties of (R)-32. Thermal stability of (R)-32 shown in thermogravimetry and differential scanning calorimetry gives the opportunity to develop innovative oral solid dosage forms loaded with this compound. The in vitro binding and functional assays indicated its multimodal mechanism of action. (R)-32, beyond TRPV1 antagonism, inhibited calcium and sodium currents at a concentration of 10 μM. Therefore, the data obtained in the current studies justify a more detailed preclinical development of (R)-32 for epilepsy and pain indications.

Lacrimal Neuralgia: A Case Report and Comprehensive Review of the Literature

PURPOSE OF REVIEW

Lacrimal neuralgia is a rare periorbital neuralgia. To date, only nine cases have been reported in the literature. Herein, we report a case and a comprehensive overview of the entity with a focus on the differential diagnosis of lacrimal neuralgia. Additionally, we propose putative diagnostic criteria for this rare neuralgia based on cases that have been reported.

RECENT FINDINGS

Among the ten cases of lacrimal neuralgia reported (including the one in this review), seven out of ten were idiopathic, and the other three were considered secondary. Most patients reported stabbing and shooting pain that was either paroxysmal or continuous. The most effective therapy was nerve block for seven patients and pregabalin for three patients. The most important clues to differentiate lacrimal neuralgia from other causes of periorbital pain include pain topography and pain with features suggestive of neuralgia. The core feature of lacrimal neuralgia is neuralgic pain located in the area supplied by the lacrimal nerve, and the etiology could be primary or secondary. Responsiveness to anesthetic blockade might better serve as a confirmational, rather than mandatory, criterion for diagnosis.

The endocannabinoid system as a therapeutic target in neuropathic pain: a review

INTRODUCTION

This review highlights the critical role of the endocannabinoid system (ECS) in regulating neuropathic pain and explores the therapeutic potential of cannabinoids. Understanding the mechanisms of the ECS, including its receptors, endogenous ligands, and enzymatic routes, can lead to innovative treatments for chronic pain, offering more effective therapies for neuropathic conditions. This review bridges the gap between preclinical studies and clinical applications by emphasizing ECS modulation for better pain management outcomes.

AREAS COVERED

A review mapped the existing literature on neuropathic pain and the effects of modulating the ECS using natural and synthetic cannabinoids. This analysis examined ECS components and their alterations in neuropathic pain, highlighting the peripheral, spinal, and supraspinal mechanisms. This review aimed to provide a thorough understanding of the therapeutic potential of cannabinoids in the management of neuropathic pain.

EXPERT OPINION

Advances in cannabinoid research have shown significant potential for the management of chronic neuropathic pain. The study emphasizes the need for high-quality clinical trials and collaborative efforts among researchers, clinicians, and regulatory bodies to ensure safe and effective integration of cannabinoids into pain management protocols. Understanding the mechanisms and optimizing cannabinoid formulations and delivery methods are crucial for enhancing therapeutic outcomes.

A Rare Case of Neuropathic Pain in Cutis Verticis Gyrata: A Review of Contemporary Literature

Cutis verticis gyrata (CVG) is a rare benign neurocutaneous condition marked by thickened scalp folds resembling cerebral gyri and sulci. It has been classified into primary essential, primary non-essential, and secondary types. The primary essential type is idiopathic, and the primary non-essential type may be associated with neurological or ophthalmological complications. Secondary CVG occurs more commonly than primary CVG, affects both genders at any age, and can be associated with endocrinal disorders, tumors, inflammatory diseases, or genetic conditions. For every 38.46 male cases, only one female case is known. This report aims to inform about a rare case of primary CVG in a 35-year-old female patient presenting with neuropathic pain localized to the affected area, a complication not previously documented in the literature. Heightened sensitivity to light touch and pinprick sensation in the high parietal scalp region was indicative of neuropathic pain. This report also highlights the importance of a multidisciplinary approach to treatment, including pharmacological treatment modalities such as analgesics and non-pharmacological management such as desensitization techniques and physical therapy. Critically, it is necessary to regularly follow up and perform proper clinical evaluation and screening to improve the quality of life for patients with CVG.

Reliability of a clinical sensory test battery in patients with spine-related leg and arm pain

BACKGROUND

The current standard to evaluate the presence of somatosensory dysfunctions is quantitative sensory testing, but its clinical utility remains limited. Low-cost and time-efficient clinical sensory testing (CST) batteries have thus been developed. Recent studies show moderate to substantial reliability in populations with neuropathic pain. This study evaluates the inter- and intra-tester reliability of people with spine-related leg and arm pain, representing mixed pain mechanisms.

METHODS

Fifty-three patients with spine-related leg (n = 41) and arm pain (n = 12) attended three CST sessions. The CST battery consisted of eleven tests, determining loss and gain of sensory nerve function. CST was performed by the same investigator twice and by an additional investigator to determine inter- and intra-tester reliability. Fleiss' (inter-tester) and Cohen's (intra-tester) kappa were calculated for dichotomized and intraclass correlation coefficients (ICC) for continuous outcomes.

RESULTS

Fleiss' kappa varied among modalities from fair to substantial (κ = 0.23-0.66). Cold, warm, and vibration detection thresholds and cold and pressure pain thresholds reached kappa >0.4 (moderate to substantial reliability). Cohen's kappa ranged from moderate to substantial (κ = 0.45-0.66). The reliability of the windup ratio was poor (ICC <0.18).

CONCLUSION

CST modalities with moderate to substantial inter-tester reliability could be of benefit as a screening tool. The moderate to substantial intra-tester reliability for all sensory modalities (except windup ratio) supports their potential use in clinical practice and research to monitor somatosensory changes over time in patients with spine-related limb pain of mixed pain mechanisms.

SIGNIFICANCE

We already know that most modalities of clinical sensory test (CST) batteries achieve moderate to substantial inter- and intra-tester reliability in populations with neuropathic pain. This study evaluates the reliability of a CST battery in populations with mixed pain mechanisms. We found inter-tester reliability varied from poor to substantial for sensory modalities, questioning the value of some CST modalities. The CST battery showed moderate to substantial intra-tester reliability, suggesting its usefulness to monitor sensory changes over time in this cohort.

Feasibility and Safety of a Home-based Electroencephalogram Neurofeedback Intervention to Reduce Chronic Neuropathic Pain: A Cohort Clinical Trial

Objective

To evaluate the feasibility, safety, and potential health benefits of an 8-week home-based neurofeedback intervention.

Design

Single-group preliminary study.

Setting

Community-based.

Participants

Nine community dwelling adults with chronic neuropathic pain, 6 women and 3 men, with an average age of 51.9 years (range, 19-78 years) and with a 7-day average minimum pain score of 4 of 10 on the visual analog pain scale.

Interventions

A minimum of 5 neurofeedback sessions per week (40min/session) for 8 consecutive weeks was undertaken with a 12-week follow-up baseline electroencephalography recording period.

Main Outcome Measures

Primary feasibility outcomes: accessibility, tolerability, safety (adverse events and resolution), and human and information technology (IT) resources required. Secondary outcomes: pain, sensitization, catastrophization, anxiety, depression, sleep, health-related quality of life, electroencephalographic activity, and simple participant feedback.

Results

Of the 23 people screened, 11 were eligible for recruitment. One withdrew and another completed insufficient sessions for analysis, which resulted in 9 datasets analyzed. Three participants withdrew from the follow-up baselines, leaving 6 who completed the entire trial protocol. Thirteen adverse events were recorded and resolved: 1 was treatment-related, 4 were equipment-related, and 8 were administrative-related (eg, courier communication issues). The human and IT resources necessary for trial implementation were identified. There were also significant improvements in pain levels, depression, and anxiety. Six of 9 participants perceived minimal improvement or no change in symptoms after the trial, and 5 of 9 participants were satisfied with the treatment received.

Conclusions

It is feasible and safe to conduct a home-based trial of a neurofeedback intervention for people with chronic neuropathic pain, when the human and IT resources are provided and relevant governance processes are followed. Improvements in secondary outcomes merit investigation with a randomized controlled trial.

Vitamin D3 Attenuates Neuropathic Pain via Suppression of Mitochondria-Associated Ferroptosis by Inhibiting PKCα/NOX4 Signaling Pathway

AIMS

Neuropathic pain remains a significant unmet medical challenge due to its elusive mechanisms. Recent clinical observations suggest that vitamin D (VitD) holds promise in pain relief, yet its precise mechanism of action is still unclear. This study explores the therapeutical role and potential mechanism of VitD3 in spared nerve injury (SNI)-induced neuropathic pain rat model.

METHODS

The analgesic effects and underlying mechanisms of VitD3 were evaluated in SNI and naïve rat models. Mechanical allodynia was assessed using the Von Frey test. Western blotting, immunofluorescence, biochemical assay, and transmission electron microscope (TEM) were employed to investigate the molecular and cellular effects of VitD3.

RESULTS

Ferroptosis was observed in the spinal cord following SNI. Intrathecal administration of VitD3, the active form of VitD, activated the vitamin D receptor (VDR), suppressed ferroptosis, and alleviated mechanical nociceptive behaviors. VitD3 treatment preserved spinal GABAergic interneurons, and its neuroprotective effects were eliminated by the ferroptosis inducer RSL3. Additionally, VitD3 mitigated aberrant mitochondrial morphology and oxidative metabolism in the spinal cord. Mechanistically, VitD3 inhibited SNI-induced activation of spinal PKCα/NOX4 signaling. Inhibition of PKCα/NOX4 signaling alleviated mechanical pain hypersensitivity, accompanied by reduced ferroptosis and mitochondrial dysfunction in SNI rats. Conversely, activation of PKCα/NOX4 signaling in naïve rats induced hyperalgesia, ferroptosis, loss of GABAergic interneurons, and mitochondrial dysfunction in the spinal cord, all of which were reversed by VitD3 treatment.

CONCLUSIONS

Our findings provide evidence that VitD3 attenuates neuropathic pain by preserving spinal GABAergic interneurons through the suppression of mitochondria-associated ferroptosis mediated by PKCα/NOX4 signaling, probably via VDR activation. VitD, alone or in combination with existing analgesics, presents an innovative therapeutic avenue for neuropathic pain.

Exploring the Therapeutic Potential of Mesenchymal Stem Cells-derived conditioned medium: An In-depth Analysis of Pain Alleviation, Spinal CCL2 Levels, and Oxidative Stress

Neuropathic pain, a debilitating condition, remains a significant challenge due to the lack of effective therapeutic solutions. This study aimed to evaluate the potential of mesenchymal stromal cell (MSC)-derived conditioned medium in alleviating neuropathic pain induced by sciatic nerve compression injury in adult male rats. Forty Wistar rats were randomly assigned to four groups: control, nerve injury, nerve injury with intra-neural injection of conditioned medium, and nerve injury with intra-neural injection of culture medium. Following sciatic nerve compression, the respective groups received either 10 µl of conditioned medium from amniotic fluid-derived stem cells or an equal volume of control culture medium. Behavioral tests for cold allodynia, mechanical allodynia, and thermal hyperalgesia were conducted, and the spinal cord was analyzed using Western Blot and oxidative stress assays. The behavioral experiments showed a decrease in mechanical hyperalgesia and cold allodynia in the group receiving conditioned medium compared to the injury group and the control medium group. Western blot data revealed a decrease in the expression of the CCL2 protein and an increase in GAD65. Oxidative stress tests also showed increased levels of SOD and glutathione in conditioned media-treated animals compared to animals with nerve injury. The findings suggest that conditioned medium derived from amniotic fluid-derived stem cells can effectively reduce neuropathic pain, potentially through the provision of supportive factors that mitigate oxidative stress and inflammation in the spinal cord.

Ultraconformable cuff implants for long-term bidirectional interfacing of peripheral nerves at sub-nerve resolutions

Implantable devices interfacing with peripheral nerves exhibit limited longevity and resolution. Poor nerve-electrode interface quality, invasive surgical placement and development of foreign body reaction combine to limit research and clinical application of these devices. Here, we develop cuff implants with a conformable design that achieve high-quality and stable interfacing with nerves in chronic implantation scenarios. When implanted in sensorimotor nerves of the arm in awake rats for 21 days, the devices record nerve action potentials with fascicle-specific resolution and extract from these the conduction velocity and direction of propagation. The cuffs exhibit high biocompatibility, producing lower levels of fibrotic scarring than clinically equivalent PDMS silicone cuffs. In addition to recording nerve activity, the devices are able to modulate nerve activity at sub-nerve resolution to produce a wide range of paw movements. When used in a partial nerve ligation rodent model, the cuffs identify and characterise changes in nerve C fibre activity associated with the development of neuropathic pain in freely-moving animals. The developed implantable devices represent a platform enabling new forms of fine nerve signal sensing and modulation, with applications in physiology research and closed-loop therapeutics.